1. Field of the Invention
The present invention relates to a temperature activated pressure relief mechanism for flashlights and other sealed battery operated devices and for batteries. More specifically, it relates to a temperature activated pressure relief mechanism which prevents explosion of a battery or sealed flashlight containing a battery which is exposed to a high temperature environment such as a fire.
2. Description of the Prior Art
It is well known that many types of batteries emit flammable or explosive gas. Because of this, many flashlight designs include gas vents, membranes or one-way valves to allow the discharge of such gas from a sealed flashlight container. It is even a specific requirement of an Underwriters Laboratory standard, namely, UL STD 913 on apparatus for use in hazardous environments which requires (18.1.3) “Compartments containing batteries which emit flammable gas shall be ventilated to prevent accumulations of ignitable concentrations.” Battery or equipment manufacturers realize that in normal operation dangerous ignitable concentrations of gas (e.g. hydrogen or methane) may build up and thus vents are known to prevent such build up.
Montelcone et al., U.S. Pat. No. 5,904,414, for example, provides a membrane to seal a vent port in the battery housing that permits flammable gas generated by the batteries within the housing to continuously escape. Wood, U.S. Pat. No. 4,237,526, provides a gas discharge vent assembly into a battery operated device which includes an aperture and a porous diffusion member.
Parker, U.S. Pat. No. 5,349,507, provides a flashlight with a complex mechanical pressure relief valve and Maglica, U.S. Pat. No. 5,113,326, and Maglica, U.S. Pat. No. 5,003,440, each provide flashlights which include a one way valve or seal to allow venting of overpressure of the interior of the flashlight.
Thus, it is well known to continuously vent pressure from a sealed battery container which is designed to operate with batteries which continuously produce flammable or explosive gas.
However, there are also other types of batteries, such as for example, lithium-iron disulfide batteries, which do not produce or emit any significant quantities of flammable or explosive gas under normal operating conditions which might pose a safety risk which would require continuous venting. Even though sealed devices which utilize such non-gas producing batteries do not require venting under normal operating conditions, venting would be required if the battery temperature becomes high enough to cause internal pressure to develop. The present invention is concerned with this latter type of battery and sealed containers therefor and is not concerned with sealed containers for gas producing batteries.
A potential problem which has not been adequately addressed in the past is that even the safer non-gas producing batteries may under extreme conditions, such as a fire or very high temperatures, develop high pressures and explode. To avoid this potential problem, most (but not all) sealed modern batteries are designed to open a vent in the battery itself at a certain temperature to relieve the internal pressure.
The existing flashlight vents, valves and permeable membranes are overly complex, potentially unreliable and overly expensive to employ and are not necessarily designed to function in this type of extreme high temperature situation.